Due to advantages such as light weight, compact volume, high power density, and high overall efficiency, permanent magnet synchronous motors (PMSMs) are widely used in various fields like hybrid electric vehicles, electric vehicles, and so forth. Control techniques are critical to exploit the power capability of PMSMs. As known, the torque generated by a PMSM may be controlled by controlling current of the PMSM because they are usually proportional. In order to effectively control the current of the PMSM, it is necessary to continuously acquire rotor position of the PMSM. It should be noted that as used herein, the term “rotor position” refers to a relative angle rather than the absolute position of the motor rotor in the PMSM. For example, the rotor position is usually defined as the leading angle between the magnetic flux linkage of the motor rotor and the α-axis in the stator frame.
In order to obtain the rotor position of the PMSM, the PMSM is usually provided with an associated resolver. A resolver is a rotatable electronic transformer, which functions as a position sensor to continuously sense the positions of the motor rotor in the PMSM. Output of the resolver is generally of a sine or cosine waveform, which can be converted into angle values in digital forms by a dedicated converter. However, since the angle value provided by the resolver indicates the absolute position of the motor rotor, it cannot be directly used as the rotor position required in PMSM control as described above. It can be appreciated that only when a zero position of the resolver of the PMSM is mechanically, strictly aligned with the zero point of control angle of the motor, the angle provided by the resolver could be directly used as the rotor position of the PMSM. However, this is nearly impossible in practice since such mechanical alignment would increase the complexity of the design and manufacturing and consume more time and manpower, thereby significantly increasing costs.
An offset between the zero position of the resolver and the control zero point of the PMSM is referred to as a resolver offset. In order to calibrate the resolver offset, a key issue is how to accurately determine such offset. Several solutions for determining the resolver offset have been proposed. For example, the offset may be estimated by measuring the back electromotive force waveform of the PMSM. The resolver offset may also be determined and calibrated by measuring the torque generated by the PMSM. However, those solutions must rely on additional circuits and/or devices, which increases costs and device dimensions and restricts the applicable fields of the PMSM. Moreover, the resolver offset determined by some known solutions often cannot meet the requirements of motor control in terms of accuracy.
In view of the foregoing, there is a need in the art for a simple, feasible, and cost-effective solution for accurately determining the offset of a resolver associated with the permanent magnet synchronous motor, in order to calibrate the resolver.